Casting wheels (or rotating launders) are commonly used in the aluminium industry. Casting wheels have also occasionally been used for the casting of ingots of other metals.
The general construction of a casting wheel includes a number of spouts (sometimes referred to as buckets) positioned on the perimeter of a wheel which is designed to rotate about its axis. The casting wheel is usually indexed to a substantially flat conveyor which includes a number of ingot moulds. The number and positioning of the spouts on the casting wheel is indexed such that each spout corresponds to one mould and allows for the filling of the mould with molten metal from the spout.
The general objective of all casting wheels is to provide an apparatus to prepare ingots of substantially equal size and weight which are free from scum and dross.
Problems associated with known casting wheels include the formation of blockages in the pouring spouts; poor design of the spouts such that the molten metal experiences excessive turbulence when poured into the mould and results in excessive dross; complex construction; and difficulty of cleaning and maintenance.
Consistent ingot weight is only achieved if spout blockages do not occur. Such blockages occur due to either oxide or dross formation. Dross formation would appear to be worse in the case of metals such as magnesium than for aluminium, although some inconsistency in operation does occur with current aluminium casting wheels.
The turbulence issue is a function of the casting wheel design, the way metal is added into the casting wheel and the location of the spout tips in relation to the height of metal in the ingot mould. Most aluminium casting wheels are of a squat cylindrical design and run with a pool of metal in an open main trough or launder. When this pool encounters a spout, metal flows into the spout and then into the mould, hopefully in such a way as the top surface skin of the metal in the pool is not disturbed. In practice, this usually means pouring more than one mould at a time. This can cause metal to flow into the mould when the spout tip is 5-10 cm above the mould bottom, causing splash and drossing.
In addition, the method of construction of the casting wheel needs to be addressed. They are usually cast from steel or iron or are fabricated from heavy gauge steel and are provided with some form of mould wash or coating. If the thermal mass of the casting wheel is too large, extensive heating of it is required to prevent freezing of the metal in the casting wheel. Known cast wheels need to have thick sections to enable them to be cast successfully. Cast wheels are normally limited production items of complex design and so the casting costs are usually high.
Further problems are observed if casting wheels are used for casting metals such as magnesium where the metal is cast under an inert or protective gas as gas heating cannot be used.
At least in preferred forms, the present invention is concerned with casting wheels, and wheel members for such wheels, which are suitable for casting magnesium or magnesium alloys.